Please, help me out here: As I posted a while ago, I had a steering issue very similar to what a couple of others are now describing. BMW replaced my entire steering column (including the EPS system) and it seemed to do the trick on the hot day I picked up the car. However, it now appears that the problem continues. There is a definite difference between the boost of the steering when the ambient temp is below about 75 degrees or above. When hot, the steering is noticeably heavier, gives less feedback, and has a “locked on center” feel. Since the whole system was replaced, I really don’t know what else it could be other than rack. I suppose it could be a mechanical binding within the rack but I don’t see how that could be temperature dependent and feels only as if the boost is reduced. I really think it has to be a design flaw in the EPS system.

I was trying o figure out how I could measure the steering boost rather than just relying on my brain determining how it felt. I initially/briefly thought about rigging up a fish weigh scale contraption, but figured that would be pretty impossible to use at speed without killing myself. And the system is designed to vary boost with speed, so I’d have to do the experiment at one particular speed in one particular curve. I see no practical/safe way of doing that. So I discovered something else:

I noticed that while on the highway, while driving through a very slight curve, if I turn the wheel (only a couple of degrees since the curve is gently) and release it, the car just tracks around the curve. In other words, the steering wheel does NOT return to the straight-ahead position when I release it mid-turn. I have done this during high temperatures and low temperatures (same road, same speed, different temperatures), and sure enough it DOES return to center (just like a “normal” car) at low temperatures.
I took the car to my dealer on a hot day and asked the service manager to drive my car (with me as the passenger). He noticed that the steering does indeed NOT return to center when the wheel is turned into a curve and released (again, I’m talking about a gentle curve). He said, “Yeah, that’s strange. On a normal car, I’d say that the rack was bad, but on this car with the EPS, I think it’s normal”. I told him that the problem is that it only does it at high temperatures. He did not believe me (And I'm sure he thought I was nuts, as I initially wondered myself). We then got into a new 2004 3.0 Sport Z4 to compare it to mine. Amazingly, it felt and behaved very similar to mine. So, perhaps they all indeed to that when it’s hot. However, I simply cannot believe that behavior is an intentional design characteristic. There is no reason for the steering boost to decrease as the ambient temperature increases. (The difference in boost/feel between hot and cold days is similar to the difference between normal and sport mode.)

This also makes me wonder about the ongoing “love it or hate it” debate on the steering. When it’s cold, I love the way my steering feels; when it’s hot, I hate it. Perhaps this is why so may people disagree.

So please conduct an experiment for me with your car. Find a section of highway that has smooth pavement and a gentle (wheel turned only a couple of degrees), constant radius curve. When the temp is low, release the steering wheel mid-turn, and see if it wants to return to center (as any “normal” car would). Then do the same on a hot day and see if the tendency to return is the same. Post your results.